#pragma ident "$Id$"

/**
 * @file SunPosition.hpp
 * Returns the approximate position of the Sun at the given epoch in the
 * ECEF system.
 */

#ifndef SUNPOSITION_HPP
#define SUNPOSITION_HPP

//============================================================================
//
//  This file is part of GPSTk, the GPS Toolkit.
//
//  The GPSTk is free software; you can redistribute it and/or modify
//  it under the terms of the GNU Lesser General Public License as published
//  by the Free Software Foundation; either version 2.1 of the License, or
//  any later version.
//
//  The GPSTk is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU Lesser General Public License for more details.
//
//  You should have received a copy of the GNU Lesser General Public
//  License along with GPSTk; if not, write to the Free Software Foundation,
//  Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110, USA
//
//  Dagoberto Salazar - gAGE ( http://www.gage.es ). 2007
//
//============================================================================


#include <cmath>
#include <string>

#include "CommonTime.hpp"
#include "Triple.hpp"
#include "GNSSconstants.hpp"
#include "AstronomicalFunctions.hpp"



namespace gpstk
{

/** @addtogroup ephemcalc */
//@{

/** This class computes the approximate position of the Sun at the
 * given epoch in the ECEF system. It yields best results between
 * March 1st 1900 and February 28th 2100.
 *
 * This is a C++ implementation version based on the FORTRAN version
 * originally written by P.T. Wallace, Starlink Project. The FORTRAN
 * version of Starlink project was available under the GPL license.
 *
 * Errors in position in the period 1950-2050 are:
 *
 * \li Maximum: 13*10^-5 AU (19200 km).
 * \li RMS: 5*10^-5 AU (7600 km).
 *
 * More information may be found in http://starlink.jach.hawaii.edu/
 */
class SunPosition
{
public:

    /// Default constructor
    SunPosition() throw() {}

    /// Destructor
    virtual ~SunPosition() {}


    /** Returns the position of Sun ECEF coordinates (meters) at the
     *  indicated time.
     *
     * @param[in]  t the time to look up
     *
     * @return  the position of the Sun at time (as a Triple)
     *
     * @throw InvalidRequest If the request can not be completed for any
     *    reason, this is thrown. The text may have additional
     *    information as to why the request failed.
     *
     * @warning This method yields an approximate result, given that
     *    pole movement is not taken into account, neither precession
     *    nor nutation.
     */
    Triple getPosition(const CommonTime& t) const
    throw(InvalidRequest);


    /** Function to compute Sun position in CIS system (coordinates
     *  in meters)
     *
     * @param t Epoch
     */
    Triple getPositionCIS(const CommonTime& t) const
    throw(InvalidRequest);


    /** Determine the earliest time for which this object can
     *  successfully determine the position for the Sun.
     *
     * @return The initial time
     *
     * @throw InvalidRequest This is thrown if the object has no data.
     */
    CommonTime getInitialTime() const throw(InvalidRequest)
    {
        return initialTime;
    }


    /** Determine the latest time for which this object can
     *  successfully determine the position for the Sun.
     *
     * @return The final time
     *
     * @throw InvalidRequest This is thrown if the object has no data.
     */
    CommonTime getFinalTime() const throw(InvalidRequest)
    {
        return finalTime;
    }


private:

    /// Time of the first valid time
    static const CommonTime initialTime;

    /// Time of the last valid time
    static const CommonTime finalTime;

}; // end class SunPosition


//@}

} // namespace gpstk
#endif  // SUNPOSITION_HPP
